The present invention relates generally to actuators, more particularly to a thermoelectric microactuator with active heating and cooling.
Actuators are well known in the art and are useful for a variety of purposes. Actuators often comprise strips that are made of two or more layers of metal that are fused together, with the metal of some or all of the layers having different temperature coefficients of expansion. When heated, the differing coefficients of expansion among the layers will cause the strip to bend, with such movement thereby actuating a subsequent operation. The more the strip is heated, the more it will bend.
One example actuator uses a bimetallic strip, with two pieces of metal having differing coefficients of expansion fused together. When an electrical current is applied to the bimetallic strip, the resulting conduction produces heat, thereby bending the strip and actuating an associated operation. Another example actuator comprises a tri-metallic strip that utilizes the Peltier effect to produce a bending motion. Thermoelectric heaters/coolers using the Peltier effect are also known in the art and are used in a variety of devices.
In 1821, T. J. Seebeck discovered that an electric current is present in a series loop of two different metals when the junction points are at different temperatures. In 1834, J. Peltier discovered that when a current is circulated through the same series loop, one junction generates heat while the other junction absorbs heat (becomes cool). When the current is reversed, the heat generating and heat absorbing junctions are reversed. Modern Peltier devices may be composed of heavily doped series-connected semiconductor segments. Such semiconductors are described, for example, in the Brun et al. U.S. Pat. No. 4,929,282, the Cauchy U.S. Pat. No. 5,448,109, and the Chi et al. U.S. Pat. No. 5,714,791.
Actuators using the Peltier effect typically comprise tri-metallic strips with a center strip of one material having one coefficient of expansion sandwiched between the outer strips of another material having another coefficient of expansion. When an electrical current is applied to the strip in one direction, the strip bends one direction, and when an electrical current is applied the strip in the opposite direction, the strip bends in the opposite direction.
Actuators utilizing metallic strips have been incorporated into many devices and have been used to control the operation of windows, ducts, fire place dampers, and fire alarms and sprinklers. While the actuators utilized by these devices work well for such applications, they are relatively large in scale. With the advent and continued advancement of micro-mechanical technology, a much smaller microactuator would be beneficial. Actuators wherein the metallic strips are electrically isolated from electrical current sources providing the means for heating and cooling would also be desirable.
The present invention provides a thermoelectric microactuator on a substrate. The microactuator includes a first temperature control element having a first surface bonded to the substrate and a second surface. A first electrically nonconductive layer has a first surface bonded to the second surface of the first temperature control element and a second surface. An actuator arm has a first region bonded to the second surface of the first electrically nonconductive layer and a flexure contiguously extending from the first region to an end cantilevered beyond the first nonconductive layer and forming an axis at the junction of the flexure and the first region. The first temperature control element controls the temperature of the actuator arm to thereby deflect the flexure about the axis.
In one embodiment, the flexure has a normal position at an ambient design temperature and the degree of deflection from the normal position is proportional to the amount that the first temperature control element varies the temperature of the actuator arm from the ambient design temperature.
In one embodiment, the actuator arm is a bimetallic strip having a first layer comprising a first metallic alloy bonded to a second layer comprising a second metallic alloy. The first metallic alloy has a first thermal coefficient of expansion and the second metallic alloy has a second thermal coefficient of expansion.
In one embodiment, a surface of the actuator arm opposite a surface of the actuator arm opposite a surface bonded to the first electrically non-conductive layer is reflective to thereby redirect an incident light wave. In one embodiment, a micromirror is bonded to the end of the flexure to thereby redirect an incident light wave. In one embodiment, an electrically nonconductive segment is bonded between the end of the flexure and an electrical contact, wherein the electrical contact makes and/or breaks external electrical circuits.
In one embodiment, the first temperature control element transfers heat to and/or from the actuator arm via the first electrically non-conductive layer. In one embodiment, the first temperature control element is a thin-film resistive layer connectable to a power source. When a current passes through the thin-film resistive layer, the thin-film layer generates and transfers heat to the actuator arm via the first electrically nonconductive layer to thereby deflect the flexure about the axis. In one embodiment, the thin-film resistive layer is a polysilicon resistor.
In one embodiment, the first temperature control element comprises a Peltier device connectable to a power source. When a current passes through the Peltier device in a first direction, the Peltier device heats the actuator arm to thereby bend the flexure about the axis in a first direction. When a current passes through the Peltier device in a reverse direction, the Peltier device cools the actuator arm to thereby bend the flexure about the axis in a direction opposite of that when the actuator arm is heated.
In one embodiment, the Peltier device comprises a p-doped segment having a first and a second end, an n-doped segment having a first and second end, and a conductor segment coupled between the first ends of the p-doped and n-doped segments. A first contact is coupled to the second end of the p-doped segment, and a second contact is coupled to the second end of the n-doped segment. When an external power supply is coupled across the first and second contacts and a current is passed through the conductor segment in a first direction, the conductor segment cools. When a current passed through the conductor segment in an opposite direction, the conductor segment generates heat.
In one embodiment, the Peltier device comprises a plurality of p-doped segments, a plurality of n-doped segments, a first plurality of conductor segments bonded to the first electrically non-conductive layer with each having a first and second end, and a second plurality of conductor segments bonded to the substrate with each having a first and second end. The first ends of the conductor segments of the first plurality are coupled to the second ends of the conductor segments of the second plurality by p-doped segments and the second ends of the conductor segments of the first plurality are coupled to the first ends of the conductor segments of the second plurality to thereby form a chain having a first and second end. A pair of contacts, one coupled to each end of the chain, is connectable to a power supply.
In one embodiment, the Peltier device comprises bizmuth telluride. In one embodiment, the first electrically nonconductive layer is an oxide insulator.
In one embodiment, the thermoelectric microactuator further comprises a second temperature control element having a first surface bonded to the substrate and a second surface, and a second electrically nonconductive layer having a first surface bonded to the second surface of the second temperature control element and a second surface bonded to the first surface of the first electrically nonconductive layer. The first temperature control element controls the temperature of the actuator arm to deflect the flexure about the axis in a first direction, and the second temperature control element controls the temperature of the actuator arm to deflect the flexure about the axis in the first direction or a second direction opposite the first direction.
In one embodiment, the first temperature control element is a thin-film resistive layer connectable to a power supply and the second temperature control element is a Peltier device connectable to a power supply. When a current passes through the thin-film resistive, the thin-film layer heats the actuator arm to thereby deflect the flexure about the axis in a first direction. When a current passes through the Peltier device in a first direction, the Peltier device heats the actuator arm to thereby deflect the flexure about the axis in a first direction, and when a reverse current passes through the Peltier device the Peltier device cools the actuator arm to thereby deflect the flexure about the axis in a second direction opposite the first direction.
In one embodiment, the second electrically nonconductive layer is an oxide insulator. In one embodiment, the Peltier device of the second temperature control element comprises bizmuth teluride.